This invention relates to the recovery of working fluid entrained in the spent geothermal brine or other hot water source withdrawn from a direct contact heat exchanger in which heat is transferred from the brine or hot water to the working fluid, and is particularly concerned with a process and system of the aforementioned type, including removal of the working fluid contained in the spent geothermal brine or hot water source, by a series of successive steps or operations, whereby the final spent brine or water removed from the system is substantially free or has a very small concentration of remaining working fluid, and wherein the working fluid so recovered is recycled to the direct contact heat exchange column.
U.S. Pat. No. 3,988,895 and applications Ser. Nos. 589,068, filed June 23, 1975, and 836,293, filed Sept. 26, 1977, by Samuel G. Woinsky, disclose recovery of energy from geothermal brine by passing such geothermal brine under pressure into direct heat exchange contact with a working fluid such as isobutane, expanding the resulting hot working fluid or isobutane in a turbine to produce work, condensing the turbine discharge, and returning the resulting condensed working fluid to the heat exchanger, and withdrawing the spent brine from the column and discarding same as by introducing the spent brine into a brine injection well.
However, dissolved and entrained working fluid usually exits the direct contact heat exchanger with the spent brine or water. If such spent brine or water containing working fluid is pumped into a rejection well or otherwise disposed of, the cost of the lost working fluid can be significant. An important consideration both for environmental and economic reasons accordingly is the recovery of the working fluid from the spent brine or hot water before discarding such brine or water, or before reinjection of spent brine into a brine injection well.
Above U.S. Pat. No. 3,988,895 discloses the step of removing entrained working fluid from the spent brine in a separator, followed by flashing off additional working fluid from the spent brine.
Above Woinsky application Ser. No. 836,293 also discloses recovery of working fluid from the spent brine in a direct contact heat exchange process and system, including removal of entrained working fluid in a separator followed by flashing off additional entrained working fluid from the spent brine.
The paper "Direct Contact Heat Exchangers in Geothermal Power Production" by I. Sheinbaum, presented at the AICHE-ASME Heat Transfer Conference, San Francisco, Cali., Aug. 11-13, 1975, suggests vacuum stripping or gas stripping of the spent hot water for recovery of working fluid. However, the use of such stripping operation requires a substantial amount of energy for removal of the dissolved and entrained working fluid.
Thus, the particular systems suggested or disclosed by the prior art for removing dissolved and/or entrained working fluid from spent brine or hot water in direct contact heat exchange processes and systems, have not been satisfactory for removing substantially all of the working fluid from the spent brine or hot water, prior to discarding same from the system, or have required the use of a substantial amount of energy for this purpose.
Accordingly, one object of the present invention is the efficient removal and recovery of working fluid entrained and/or dissolved in the spent geothermal brine or hot water withdrawn from a direct contact heat exchanger used for recovery of energy from such geothermal brine or hot water. Another object is the provision of an economical process and system of the above type, including subjecting the spent brine or hot water from the direct contact heat exchanger to a series of successive operations or steps, for removal of substantially all of the entrained working fluid from the spent brine or hot water and for recycling of such recovered working fluid to the direct contact heat exchanger. A still further object of the invention is the carrying out of such operations or steps for recovery of working fluid contained in the spent brine or hot water, with a minimum energy expenditure.